1. Field of the Invention
The present invention relates to a method and apparatus for measuring a biological function of a subject, e.g., a cardiac amplitude image and/or a cardiac phase image of the subject, using radiation, and more particularly to such a method and apparatus employing digital image processing.
2. Description of the Prior Art
A conventional radiation diagnostic apparatus, e.g., an X-ray diagnostic apparatus for obtaining X-ray images of circulatory organs by using an X-ray contrast medium, is disclosed as in U.S. Pat. No. 4,204,225 and U.S. Pat. No. 4,204,226 to Mistretta issued on May 20, 1980.
In an apparatus of this type, a digitally subtracted image is obtained between a mask image, i.e., an X-ray image taken before injection of an X-ray contrast medium to the circulatory organs, and a contrast image, i.e., an X-ray image taken after injection, so as to diagnose a region of interest in the circulatory organs.
However, in such an apparatus, it is very difficult to evaluate the biological cardiac function, i.e., cardiac amplitude and cardiac phase, etc., as the cardiac movement. It is impossible to evaluate the biological function quantitatively because, in the above conventional apparatus, an operator only observes the successive cardiac movement images on a monitor.
Furthermore, in a conventional apparatus, digital arithmetic operations such as addition or subtraction of the acquired images taken before and after injection of the X-ray contrast medium are performed on these images without taking account of natural pulsations of the circulatory organs. For this reason, undesirable artifacts occur due to differences among the cardiac beat phases in the diagnostic images. In addition, since an improvement of the concentration resolution is performed by adding images of different cardiac beat phases, the spatial resolution of these added images becomes low. Therefore, evaluating the biological function is hampered.
In the field of the nuclear medicine diagnosis, the journal titled "Kakuigaku" (produced by Hisato Maeda et al), the 19th, No. 5, pages 765-776, discloses a software method for obtaining the cardiac amplitude image and the cardiac phase image as a nuclear medicine image (i.e., a radioisotrope distribution image) using Fourier function development.
However, in the collection and preprocessing of images there is a difference between a digital fluoroscopy and the nuclear medicine.